LTE can mooch off of Wi-Fi spectrum with new Qualcomm chipset

A chipset Qualcomm is introducing at Mobile World Congress next week is likely to make mobile operators happy and some Wi-Fi fans nervous.

Amid a scramble for spectrum among cellular carriers, Qualcomm will demonstrate a chipset that lets LTE cells operate in a radio band used by Wi-Fi networks. The new silicon could double the amount of spectrum subscribers can use in certain areas, and it's just the first in a family of chipsets that may eventually tap into five times as much.

The FSM 99xx chipset for small cells, along with a matching transceiver that will go into mobile devices, are among the first products coming for so-called Licensed Assisted Access. LAA, sometimes called LTE-Unlicensed, is one of several emerging techniques to take advantage of the large amount of spectrum available in unlicensed bands used by Wi-Fi. Verizon Wireless, T-Mobile USA and SK Telecom all have shown interest in using LAA. Combining unlicensed spectrum with traditional carrier frequencies will be a major trend on display at MWC.

The benefit of unlicensed spectrum is that it's free for anyone to use, so carriers can tap into it without paying billions in an auction or going through a long licensing process. But that's also what makes it risky, according to the Wi-Fi Alliance. The industry group fears that without the right safeguards, LTE networks could hurt Wi-Fi performance. It's working with the 3GPP cellular standards group on future rules to prevent interference.

Qualcomm says its product is ready to be a good neighbor. Tests at Qualcomm showed that putting up a cellular base station built with the new chipset won't affect nearby Wi-Fi users any more than adding another Wi-Fi access point would, said Mazen Chmaytelli, senior director of business development at Qualcomm. It plans to offer products with future safeguards once they're finished but says they aren't needed to keep Wi-Fi safe.

LAA uses the 5GHz band, the biggest one for Wi-Fi. The system won't let carriers set up LTE networks that just use unlicensed spectrum. It's designed to add some spectrum to a regular licensed network where necessary, and only for downstream traffic. All the data going out to the Internet from the phone still goes over LTE.

Qualcomm says LAA a better alternative to the Wi-Fi hotspots that many carriers install to offload traffic in busy areas. For one thing, Qualcomm tests have shown it's at least twice as efficient, said Mazen Chmaytelli, senior director of business development at Qualcomm. LTE can carry more data with the same amount of spectrum than Wi-Fi can, so it can give users a bigger performance boost. Also, subscribers stay on the cellular network while they use LAA, so they don't have to go through a handoff to a different network, Chmaytelli said.

The Qualcomm chipset uses carrier aggregation, a part of the LTE-Advanced specification that carriers are already using to glue together different chunks of licensed spectrum. Initial deployments will combine 20MHz of licensed spectrum with 20MHz from the unlicensed band. Later, it will be possible to aggregate several times that much spectrum for a bigger performance boost, Chmaytelli said.

In some regions, carriers may start putting up LAA cells in the first half of next year, he said. Those in Japan and Europe have to wait for new rules being written for the next version of LTE to account for a "listen before talk" requirement for unlicensed spectrum there. Chmaytelli expects those carriers to start rolling out networks 12 to 18 months later.

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